I work at the college and worked on the appearance; the Ford Fieldhouse capacity according to the fire codes is 4,000. From what I saw, 4,000 is a generous estimate of how many people attended.
The stage for the Bush was at the north end of the fieldhouse. There were bleachers behind the stage and lecturn, as well as bleachers flanking the stage on either side and extending out into the floor. There were also chairs in the front of the stage, and the press section was directly behind the chairs on the floor (the press had a few rows of chairs for print media, and the TV media had a three-level platform to set tripods up on).
That's not to say that more people weren't interested in going; certainly there were - but it was a more small, intimate appearance and only a very limited number of tickets were made available to the general public.
It seemed to me that every possible seat was filled, they were even letting people sit in the press area. So 4000 is a good number for the Presidents event. Matter of fact, it was announced as 4500 at the Kerry rally.
Either way, lets see what happens at the Iowa rally. Both candidates will be just 2 blocks apart.
Bring it on!